isPrime works but UnBoundLocalError when mapping on list

defn noob circularfunc at yahoo.se
Tue Jul 15 19:36:23 CEST 2008


On Jul 15, 7:28 pm, Mensanator <mensana... at aol.com> wrote:
> On Jul 15, 11:26 am, defn noob <circularf... at yahoo.se> wrote:
>
>
>
> > isPrime works when just calling a nbr but not when iterating on a
> > list, why? adding x=1 makes it work though but why do I have to add
> > it?
> > Is there a cleaner way to do it?
>
> > def isPrime(nbr):
> >     for x in range(2, nbr + 1):
> >         if nbr % x == 0:
> >             break
> >     if x == nbr:
> >         return True
> >     else:
> >         return False
>
> > >>> [isPrime(y) for y in range(11)]
>
> > Traceback (most recent call last):
> >   File "<pyshell#45>", line 1, in <module>
> >     [isPrime(y) for y in range(11)]
> >   File "C:\Python25\Progs\blandat\myMath.py", line 9, in isPrime
> >     if x == nbr:
> > UnboundLocalError: local variable 'x' referenced before assignment
>
> > >>> map(isPrime, range(100))
>
> > Traceback (most recent call last):
> >   File "<pyshell#38>", line 1, in <module>
> >     map(isPrime, range(100))
> >   File "C:\Python25\Progs\blandat\myMath.py", line 9, in isPrime
> >     if x == nbr:
> > UnboundLocalError: local variable 'x' referenced before assignment>>> isPrime(10)
> > False
> > >>> isPrime(11)
>
> > True
>
> > adding x=1 makes it work though:
>
> > def isPrime(nbr):
> >     x=1
> >     for x in range(2, nbr + 1):
> >         if nbr % x == 0:
> >             break
> >     if x == nbr:
> >         return True
> >     else:
> >         return False
>
> > >>> [isPrime(y) for y in range(11)]
>
> > [False, True, True, True, False, True, False, True, False, False,
> > False]
>
> No, it doesn't. You are falsely reporting that 1 is prime.
>
> And instead of making the fake variable x, shouldn't you
> instead test that nbr+1 is greater than 2? Or call it with
> range(3,11) instead of range(11)? x isn't initialized
> because if nbr+1 is <=2, the for loop has an invalid range
> and doesn't even execute.


def isPrime(nbr):
    for x in range(2, nbr + 1):
        if nbr % x == 0:
            break
    if x == nbr:
        return True
    else:
        return False

this works for all primes, if i want to not include 1 i just do if
nbr<=1 return false

you are answering the wrong question.


anyway here is a clear one:
def isPrime(nbr):
    if nbr < 2:
        return False
    for x in range(2, nbr + 1):
        if nbr % x == 0:
            return nbr == x



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